Check Control Center

Touch and hold the bottom of the watch face, wait for Control Center to show, then swipe up. Tap the highlighted Do Not Disturb and Airplane Mode icons to turn off the settings.

Check your connection

Make sure that your Apple Watch can connect to your iPhone, cellular, or Wi-Fi. To send and receive SMS/MMS from cellular models of Apple Watch, your paired iPhone must be powered on and connected to Wi-Fi or cellular, but your iPhone doesn’t need to be nearby.

Even if your iPhone isn’t connected or powered on, you can send and receive iMessages on your Apple Watch when your Apple Watch is connected to Wi-Fi or cellular.